//计算服务器消耗时长的js

module.exports = async (ctx, next) => {
    //记录开始时间
    const start = Date.now();
    //让内层中间件得到执行
    await next()
    //记录结束时间
    const end = Date.now();
    //设置响应头 X-Response-Time
    const duration = end - start
    //ctx.set设置响应头
    ctx.set('X-Response-Time', duration + 'ms')

}